Method and apparatus for making twisted stonesawing strands and the like

ABSTRACT

A single strip is twisted about its axis or a plurality of strips are twisted together with the direction of twist in each case being reversed at spaced intervals such as 25 feet, 50 feet or 100 feet. An entry tensioning stand, a twister head stand and an exit tensioning stand are arranged in tandem with strip gripping means being provided on each stand. The gripping means on each tensioning stand is mounted on a longitudinally movable slide which is attached to a pair of pneumatic cylinders for urging the slide away from the twister head stand under a predetermined pressure when the strip is gripped with equal lengths on each side of the twister head. The length on one side will be twisted opposite hand to the length on the other side as the twister head rotates with a predetermined tension being applied to the strip as it is twisted regardless of change of length during the twisting operation. The strip is then released and the strip fed longitudinally until the twisted portion is just past the gripping means on the exit tensioning stand. The twisting operation is then repeated. This continues until all the strip is twisted.

United States Patent Blanchet et al.

[451 Dec.5, 1972 [54] METHOD AND APPARATUS FOR MAKING TWISTED STONESAWING STRANDS AND THE LIKE [72] Inventors: Raymond J. Blanchet, North Branford; William G. Stanton, North Haven, both of Conn.

[73] Assignee: United States Steel Corporation [22] Filed: July 26, 1971 [2]] Appl. No.: 166,047

[52] U.S. Cl ..57/34 AT, 57/156 [51] Int. Cl. ..D01h 7/00 [58] Field of Search ..57/l R, 34 R, 34 AT, 59, 60,

Primary Examiner-Werner H. Schroeder Attorney-Martin J. Carroll [57] ABSTRACT A single strip is twisted about its axis or a plurality of strips are twisted together with the direction of twist in each case being reversed at spaced intervals such as 25 feet, 50 feet or 100 feet. An entry tensioning stand, a twister head stand and an exit tensioning stand are arranged in tandem with strip gripping means being provided on each stand. The gripping means on each tensioning stand is mounted on a longitudinally movable slide which is attached to a pair of pneumatic cylinders for urging the slide away from the twister head stand under a predetermined pressure when the strip is gripped with equal lengths on each side of the twister head. The length on one side will be twisted opposite hand to the length on the other side as the twister head rotates with a predetermined tension being applied to the strip as it is twisted regardless of change of length during the twisting operation. The strip is then released and the strip fed longitudinally until the twisted portion is just past the gripping means on the exit tensioning stand. The twisting operation is then repeated. This continues until all the strip is twisted.

18 Claims, 22 Drawing Figures PATENTEDMB film 3.704.580

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RAYMOND J. BLANUHETa/rd WILLIAM G. STANTON Meir Aflorney SHEET 0F 5 P'A'TENTED 0H: 5 I972 Meir Attorney PATENTED 5 I973 SHEET 5 BF 5 m& mm

5 wa mufim INVENTORS RAYMOND J. BLANCHET and WILLIAM G. STANTON "1M M S .COJULa-QVQ Meir Attorney METHOD AND APPARATUS FOR MAKING TWISTED STONESAWING STRANDS AND THE LIKE This invention relates to a method and apparatus for making elongated twisted objects having the direction of twist reversed at intervals and, more particularly, for making stone sawing strands. Stone sawing strands may be made from a single strip twisted about its axis such as those shown in DAvocourt US. Pat. No. 2,003,994, dated June 4, 1935, and Stevens US. Pat. No. 2,876,761, dated Mar. 10, 1958 The strip may be either rectangular or of various shapes. Other stone sawing strands have two or more wires or strips twisted together as shown in LI-Ioir et a1. U.S. Pat. No. 626,621, dated June 6, 1899, and Dessureau et al. US Pat. No. 2,856,914, dated Oct. 21, 1958. In all of these strands direction of twist is reversed at intervals. For example, it is common to have the direction of twist reversed every 25, 50 or 100 feet. Apparatus for twisting a single strip is shown in DAvocourt US. Pat. No. 2,616,478, dated Nov. 4, 1952. However, to the best of our knowledge, this apparatus has not been used in making multi-strip stone sawing strands. This apparatus is relatively slow and requires considerable manual operation. It is also very difficult or impossible to vary the distance between reversals. The tension applied to the strip varies during the twisting operation and it is difficult to vary the amount of tension for different materials.

It is, therefore, an object of our invention to provide apparatus which makes elongated twisted objects at substantially greater speeds than the apparatus previously used.

Another object is to provide such apparatus which greatly reduces the amount of manual work necessary to produce the twisted object.

Still another object is to provide such apparatus which enables the distance between reversals to be readily changed and which also produces a strand having an improved reversal section.

A further object is to provide such apparatus in which the tension is maintained uniform throughout the twisting operation and in which the tension may be varied as desired for a particular product.

A still further object is to provide an improved method of making such objects regardless of whether the objects are made of a single or multiple strips.

These and other objects will become more apparent after referring to the following specification and at tached drawings, in which:

FIG. I is a side elevation of the apparatus of our invention;

FIG. 2 is a schematic plan view showing the location of foundations and piping;

FIG. 3 is a side elevation of the entry tensioning stand;

FIG. 4 is a plan view of FIG. 3;

FIG. 5 is an end elevation of FIG. 3;

FIG. 6 is a view taken on the line VIVI of FIG. 4;

FIG. 7 is an enlarged view of a portion of FIG. 6 with parts broken away and shown in section;

FIG. 8 is a side elevation of the twister head system;

FIG. 9 is a view taken on the line IX-IX of FIG. 8;

FIG. 10 is a side elevation, partly in section, showing the jaws in clamping position;

FIG. 11 is a view showing a portion of FIG. 10, but with the jaws open;

FIG. 12 is a side elevation of the exit tensioning stand;

FIG. 13 is a plan view of FIG. 12;

FIG. 14 is an end view of FIG. 12;

FIG. 15 is a view taken on the line XVXV of FIG. 12;

FIG. 16 is a view taken on the line XVI-XVI of FIG. 15'.

FIG. 17 is a view taken on the line XVII-XVII of FIG. 16;

FIG. 18 is a view taken on the line XVIIIXVII of FIG. 17;

FIG. 19a, 19b and 19c show schematically the pneumatic system of our invention; and

FIG. 20 is a schematic wiring diagram used with our invention.

Referring more particularly to FIGS. I and 2 of the drawings, reference numeral 2 indicates a pay-off reel for supporting a coil of flat steel strip 8. The strip S passes from the pay-off reel 2 to an entry tensioning stand 4, then to a twister head stand 6 from which it passes to an exit tensioning stand 8, and finally to a take-up reel 10 driven by motor 11. These components are broadly the same as in DAvaucourt US. Pat. No. 2,616,478, but the construction of stands 4, 6 and 8 are different than in the patent. The reels 2 and 10 are permanently fixed, but the location of the stands preferably are variable. For this purpose, five spaced apart foundations l2, l3, 14, 15 and 16 are provided. These foundations are identical and include 3 pairs of threaded studs 18, the threaded portion of which extend above the floor level and are adapted to receive nuts 20. The number of foundations may vary depending upon the number of different lengths of reversals desired. In one particular installation the location of the foundations are as indicated in FIG. 2. It will also be understood that female sockets could be used in place of studs 18 and cap screws or the like threaded into the sockets.

Each tensioning stand 4 (FIGS. 3, 4 and 5) and 8 (FIGS. 12, I3 and 14) includes a fabricated steel base 22 consisting of horizontal steel plates 24 and 26 connected by vertical steel plates 28 and spaced apart channels 30 mounted on top of plate 26. Spaced apart inverted channels 31 extend through holes 32 in plates 28. The channels and plates are preferably connected by welds. Holes 33 are provided in plate 24 for receiving the studs 18. A pair of air cylinders 34 are mounted on top of channels 30 with their axes substantially parallel to the path of travel of strip S and their blind end adjacent stand 6. A strip guide plate 36 is attached to base 22 on the side toward stand 6. Spaced apart guides 38 (FIGS. 3 to 7) are provided on top of channels 30 of stand 4 for slidably receiving a clamp slide 40 which is secured to piston rods 42. The slide 40 has a vertical opening 44 therein with a bottom clamp member 46 secured in the bottom thereof. A strip receiving slot 48 is provided in the upper portion of member 46. A movable top clamp member 50 is slidably mounted in vertical opening 44. The member 50 has a tongue 52 adapted to enter slot 48. The member 50 is connected to piston rod 54 of a vertical air cylinder 56.

Spaced apart guides 58 (FIGS. 12 to 18) are provided on top of channels 30 of stand 8 for slidably receiving a clamp slide 60 which is secured to piston rods 42. The slide has a vertical opening 62 therein for receiving top and bottom grip holders 64 and 66, which are identical. Each holder includes four bottomed holes 68 for receiving springs 70 to bias the holders apart. An undercut groove 72 is provided in each holder for receiving a resilient grip 74 made of elastomeric solid polyurethane, as in US. Pat. No. 2,729,618. A guide 76 is secured to the rear of each of the holders 64 and 66 and a guide 78 to the front of each of the holders. Each of the guides 78 has a vertical hole 80 therein aligned with the hole 80 in the other guide. A flip pin or clamp 82 is received in each hole 80 and has a beveled strip bearing surface 84 on its inner end. A spring 86 surrounding the outer end of each clamp 82 urges the clamps toward one another. Piston rods 88 of the top and bottom pneumatic cylinders 90 mounted on clamp slide 60 bear against the members 64 and 66 to urge them together.

The stand 6 (FIGS. 8 to 11) includes a fabricated steel base 92 having three pairs of holes 94 at its bottom for receiving the studs 18. Lifting lugs 96 are provided at the entry end of the base with aligned holes 98 being provided therein. Aligned holes 100 are provided in the sides of the base at its exit end. A motor 102 mounted on stand 6 drives a pulley 104 through a device 106 having a clutch and brake incorporated therein with the clutch being provided with a solenoid 106C and the brake with a solenoid 106B. This may be an ELECTRO-PACK. A pair of bearings 108 are supported on a pedestal 110 which in turn is mounted on base 92. A twister rotor 112 mounted in bearings 108 has a pulley 114 at one end which is driven from pulley 104 by belt 116. The rotor 112 has an axial opening 118 therethrough with a reduced diameter guide portion 120 intermediate its ends. A vertical radial hole 122 extends from the portion 120 to the outside of the top and bottom of the rotor to receive top and bottom clamps 124 each of which carries a roller 126 at its outer end with the axes of the rollers being horizontal and transverse to the axis of hole 118. The inner end of each clamp has a beveled gripping surface 128. A spring 130 surrounds each clamp 124 with its ends bearing against shoulders 132 and 134 to urge the clamp outwardly. A pressure member 136 surrounds the rotor 112 and is kept from rotating by a spline connector 138. The member 136 has a cup portion 140 having an internal tapered surface 142 which contacts rollers 126. The member 136 also has a peripheral groove 144 which receives two roller followers 146 each mounted on the outer end of a lever arm 148. The arms 148 are secured to a pivot pin 150 which is rotated by arms 152 secured to a pneumatic cylinder 154 having its piston rod 156 pivotally mounted on pin 158. The parts 148, 150 and 152 form a lever assembly which is movable by movement of cylinder 154 to move pressure member 136 to and from clamping position. The strip which may be at any angle is received between the tapered bearing surfaces of the twister an take-up clamps and as the clamps tighten on the strip the tapered surfaces turn the strip until it is clamped sec'urely therebetween.

Arranged along the length of the equipment are four manifold pipe lines 161, 162, 163 and 164 (FIGS. 2, 19a, 19b and 19c) having a plurality of sets of sockets (shown as five) 161s, 162s, 163s and 164s spaced apart along their length one set adjacent each foundation 12 to 16. Four sets of flexible conduits 161c, 162c, 1630 and 164a are received in four of the sets of sockets. in our particular installation the sockets at the extreme left (FIG. 2) are used at all times because the operator is most often in this position and a control stand 166 is provided at this point. To prevent mistakes a different type of socket connection is used for each of the four pipes. Air supply for all of the cylinders are provided from a conduit 168 at control stand 166 (FIG. 19b). The air passes from pipe 168 to line 161 through a three-position detent lever operated, four-way valve 170 and to line 162 through a two-position lever operated, pilot return, four-way valve 172 and a flow control valve 174. A check valve 176 is arranged in parallel with valve 174. At the desired position line 162 is connected to the rear end of cylinder 154 through a control valve 178 connected in parallel with check valve 180. A sequence valve 182 is connected to the flexible conduit 162C between cylinder 154 and valve 178 and is adapted to supply pilot air to line 164 through flexible conduit 164C when the pressure in cylinder 154 reaches a predetermined level.

At the desired position adjacent entry stand 4, line 162 is connected through flexible conduit 162C to the rear end of cylinder 56 (FIG. 19a) and the front end of cylinder 56 is connected to line 163 through flexible conduit 163C. At this same position line 163 is connected to the front end of cylinders 34 through flow control valve 184 and check valve 186 connected in parallel, and through a two-position cam actuated fourway valve 188. A control valve 189 and check valve 190 are connected in parallel in conduit 161C to the rear end of cylinders 34. A cam 191 connected to slide 40 moves the valve 188 to different position against the pressure of spring 1888. There is also a by-pass connecting line 192 around valve 188 through a check valve 194. A two-position pilot operated four-way valve 196 is connected to lines 163 and 164 through flexible conduits 163C and 164C and also is connected to line 192.

At the desired location adjacent exit stand 8, line 162 is connected to the rear ends of cylinders 90 (FIG. 19c) and line 163 is connected to the front ends of cylinders 90. Line 161 is connected to the rear ends of cylinders 34 through control valve 198 and check valve 200 connected in parallel. Line 163 is connected to the front end of cylinder 34 through control valve 202 and check valve 204 connected in parallel and through a valve 206 of the same type as valve 188. The valve 206 is positioned by means of a cam 208 connected on slide 60. A valve 210 of the same type as valve 196 is connected to line 164 and also to line 163. A connection 212 having a check valve 214 therein by-passes valve 206 and also has a connection to valve 210.

As shown the clamps will be open and the slides 40 and 60 will be moving away from one another. This is because pressure air is being delivered to the rear ends of the cylinders 34. When the slides reach their midposition the cams 191 and 208 will shift the position of valves 188 and 206 until they shut off flow of air from the cylinders 34. The operator by positioning valve 172 to permit flow of pressure air from conduit 168 to line 162 then causes air to be supplied to the rear ends of cylinders 56, 90 and 154 to move all the clamps to clamping position. The valve 182 then opens to supply pilot air to line 164 which positions valves 196 and 210 to permit the air on the front ends of cylinder 34 to exhaust, thus permitting their piston rods and attached slides to be moved by the strip S as its length varies.

The operator takes pressure off the clamp cylinders by moving valve 172 to the position shown. He then moves valve 170 to connect conduit 168 to line 163. This supplies pressure air to the front end of cylinders 56, 90 and 154 to retract their respective clamps. Release of pressure from the rear end of cylinder 154 shuts off the pilot air and application of air through line 163 moves valves 196 and 206 to their original posi tion. Pressure air to line 161 is also shut off by movement of valve 170 to this position so that there is no pressure supplied by cylinders 34.

Power is applied to take-up motor 11 (FIG. 20) from power lines Ll-L2 through a switch 216 and motor control 218. Power is applied to clutch solenoid 106C and brake solenoid 1068 from power lines L1-L2 through switches 220 and 222, respectively. Power is applied to motor 102 through switch 224 and motor control 226.

The operation of our device is as follows:

The twister head stand 6 is placed on the desired foundation to obtain the desired distance between reversals. In the particular installation shown in FIG. 2, 25 ft., 50 ft., or 100 ft. reversals may be made. Assuming that a stone sawing strand having reversals at 100 ft. is desired the stand 6 will be placed on foundation 15. This may be done by a crane attaching hooks and chains into the holes 98 and 100 moving the stand 6 above the foundation l5 and lowering it until the studs 18 are received in holes 94. Nuts 20 are then threaded onto the studs 18 to lock the stand in position. The stands 4 and 8 are then positioned on foundations 12 and 16, respectively. This is done by essentially the same manner as for stand 6 with holes 32 being used for lifting purposes. With these stands a fork lift truck may be used. The flexible conduits 161C, 162C, 163C and 164C are connected to the sockets at the location of foundations 12, 15 and 16. For 50 ft. and 25 ft. reversals, stand 8 is left on foundation 12. For 50 ft. reversals stand 4 is placed on foundation 15 and stand 6 on foundation 14. For 25 ft. reversals stand 4 is placed on foundation 14 and stand 6 on foundation 13. The conduits 161C, 162C, 163C and 164C are connected adjacent the appropriate foundation. The operation then proceeds in the following manner:

A strand or strip S is fed from the pay-off reel 2 and fed through the stands 4, 6 and 8 to the take-up reel 10. The operator then moves valve 170 to the position shown which applies pressure to the rear ends of cylinders 34 to cause the slides 40 and 60 to move away from stand 6 until they become locked in a centered position on their guides. The operator then positions valve 172 to cause flow of air to the rear ends of cylinder 56, 90 and 154 to clamp the strand S in place. This opens valve 182 to supply pilot air to valves 196 and 210 to permit movement of the pistons of cylinders 34. The operator then closes switches 220 and 224 to engage clutch 107 and start motor 102. Since there is a predetermined air pressure in each cylinder 34 the strand S will be under the desired tension. As the rotor rotates the portion of the strand S between the center clamp and entry clamp will be twisted one way and that between the center clamp and exit clamp will be twisted opposite hand so that there is a point of reversal at the center clamp. Regardless of whether or not the length of the strand changes as it is rotated the same tension will be applied thereto because of the predetermined air cylinders 34. After a predetermined number of revolutions the motor 102 is stopped, the clutch 107 disengaged and the brake 108 engaged. The brake is then momentarily released to let the strand take its own set and then re-engaged. This is preferably done automatically. The valves 172 and 170 are then positioned to supply air to the front of cylinder 59, and 154 to release the clamps. This also causes valves 196 and 206 to return to their original position.

Motor 11 is then operated to draw 200 ft. of strand through the line. The above operation is then repeated. This continues until the entire length of strand is twisted.

The operation is essentially the same when twisting two or more strip or wires together. In some instances it would be desirable to change the shape of the clamp gripping surfaces to better clamp the workpiece. The multiple strip lengths are fed side by side into the line either from a single pay-off reel or from a pay-off reel for each length of strip. The term strip as used herein covers an elongated workpiece of any cross-sectional shape such as those shown in the various patents referred to herein.

While several embodiments of our invention have been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

We claim:

1. The method of making an elongated twisted object having the direction of twist reversed at intervals which comprises feeding the number of strips desired in the finished object longitudinally through a twister head in untwisted form until a substantial length of the untwisted strip is beyond the twister head, then gripping the strip at the twister head and at a substantial distance from the twister head at the entry and exit ends thereof to prevent movement of the strip with respect to the grips, then applying a resilient force to said strip at each of the entry and exit gripping positions to provide a predetermined tensioning force to said gripped strip, then rotating said twister head a predetermined number of times with the strip gripped and under said predetermined tension, then releasing said gripped strip and feeding the strip longitudinally through said twister head until a substantial length of said untwisted strip is beyond the twister head, then gripping the strip at the twister head, at the exit head adjacent the twisted portion of said strip and at a substantial distance from the twister head at the entry thereof to prevent movement with respect to the grips, and then releasing said gripped strip.

2. The method of claim 1 in which the distance between the grip at the twister head and the grip at the entry end is the same as the distance between the grip at the twister head and the grip at the exit end.

3. The method of claim 2 in which the grips at the entry and exit ends are free to move longitudinally as the strip is twisted while maintaining the predetermined tension.

4. The method of claim 1 in which a single strip is twisted about its axis.

5. The method of claim 4 in which the distance between the grip at the twister head and the grip at the entry end is the same as the distance between the grip at the twister head and the grip at the exit end.

6. The method of claim 5 in which the grips at the entry and exit ends are free to move longitudinally as the strip is twisted while maintaining the predetermined tension.

7. The method of claim 1 in which a plurality of strips are twisted together.

8. The method of claim 7 in which the distance between the grip at the twister head and the grip at the entry end is the same as the distance between the grip at the twister head and the grip at the exit end.

9. The method of claim 8 in which the grips at the entry and exit ends are free to move longitudinally as the strip is twisted while maintaining the predetermined tension.

10. Apparatus for making an elongated twisted object having the direction of twist reversed at intervals which comprises an entry tensioning stand including strip gripping means, a twister head stand on the exit side of said entry tensioning stand including strip gripping means, an exit tensioning stand on the exit side of said twister head stand including strip gripping means, means for feeding the number of strips desired in the finished object through said stands, said strip being in untwisted form prior to being fed into and gripped by said strip gripping means, resilient means on each of said entry and exit tensioning stands urging their strip gripping means away from said entry tensioning stand to provide a predetermined tensioning force to the strip when clamped by all of said strip gripping means and means for rotating said strip gripping means.

11. Apparatus according to claim 10 in which each of said tensioning stands includes guides mounted thereon, and a slide supporting said gripping means slidably mounted for longitudinal movement in said guides, said resilient means including a pair of air cylinders having their axes substantially parallel to the path of travel of said strip and their piston rods connected to said slide.

12. Apparatus according to claim 11 in which said entry gripping means includes a pair of opposed clamp members, and an air cylinder and piston rod for moving said clamp members with respect to one another, and in which said exit clamping means includes a pair of opposed clamp members each having a beveled strip bearing surface on its inner end, a spring urging each of said clamp members inwardly toward one another, a pair of elongated grip holders on the exit side of said clamp members and one secured for movement with each of said clamp members, springs for biasing said grip holders apart. a resilient grip attached to each grip holder, and an air cylinder and piston rod associated with each grip holder for moving then together.

13. Apparatus according to claim 12 in which said twister head stand comprises a twister rotor having an axial hole therethrough, and means for rotating said rotor; and said twister head stand gripping means including a pair of opposed radial clamping members one on each side of said axial hole and each having a beveled gripping surface, a roller mounted on the outer end of each radial clamping member with the axis of each roller being transverse to the axis of sad rotor hole, a

spring urging each clamp member outwardly, a pressure member slidably mounted on said rotor having a cup portion with an internal tapered surface for contacting said rollers and a peripheral groove, a pair of spaced rollers in said peripheral groove, a lever assembly for supporting said spaced rollers, and an air cylinder and piston rod associated with said lever for moving said pressure member to move said clamping members to clamping position.

14. Apparatus according to claim 13 including a pneumatic control system, said pheumatic control system comprising means for supplying air to said tensioning cylinders to move said slides to their centered position, means then operable for supplying air to said clamping cylinders to cause said clamping means to grip untwisted strip extending between said entry and exit tensioning stands, means then operable to cause air at a predetermined pressure to be present only on the side of the cylinder pistons urging said slides away from the twister head stand, and means operable after twisting of said strip to cause opposite movement of said clamping cylinders to release said strip.

15. Apparatus according to claim 13 including a payoff reel at the entry end of said entry tensioning stand for supporting said strip in untwisted form, a take-up reel at the exit end of said exit tensioning stand for supporting said twisted object, and at least four foundations spaced apart between said reels for selectively receiving said stands.

16. Apparatus according to claim 15 including a pneumatic control system, said pneumatic control system comprising means for supplying air to said tensioning cylinders to move said slides to their centered position, means then operable for supplying air to said clamping cylinders to cause said clamping means to grip untwisted strip extending between said entry and exit tensioning stands, means then operable to cause air at a predetermined pressure to be present only on the side of the cylinder pistons urging said slides away from the twister head stand, and means operable after twisting of said strip to cause opposite movement of said clamping cylinders to release said strip.

17. Apparatus according to claim 16 in which said pneumatic control system includes four manifold pipe lines extending adjacent said foundations and having a set of sockets adjacent each foundation, a control stand having connections to one set of sockets, and flexible connections between each of said stands and the adjacent set of sockets.

18. Apparatus according to claim 10 including a payoff reel at the entry end of said entry tensioning stand for supporting said strip in untwisted form, a take-up reel at the exit end of said exit tensioning stand for supporting said twisted object, and at least four foundations spaced apart between said reels for selectively receiving said stands.

* i I! t 1! 

1. The method of making an elongated twisted object having the direction of twist reversed at intervals which comprises feeding the number of strips desired in the finished object longitudinally through a twister head in untwisted form until a substantial length of the untwisted strip is beyond the twister head, then gripping the strip at the twister head and at a substantial distance from the twister head at the entry and exit ends thereof to prevent movement of the strip with respect to the grips, then applying a resilient force to said strip at each of the entry and exit gripping positions to provide a predetermined tensioning force to said gripped strip, then rotating said twister head a predetermined number of times with the strip gripped and under said predetermined tension, then releasing said gripped strip and feeding the strip longitudinally through said twister head until a substantial length of said untwisted strip is beyond the twister head, then gripping the strip at the twister head, at the exit head adjacent the twisted portion of said strip and at a substantial distance from the twister head at the entry thereof to prevent movement with respect to the grips, and then releasing said gripped strip.
 2. The method of claim 1 in which the distance between the grip at the twister head and the grip at the entry end is the same as the distance between the grip at the twister head and the grip at the exit end.
 3. The method of claim 2 in which the grips at the entry and exit ends are free to move longitudinally as the strip is twisted while maintaining the predetermined tension.
 4. The method of claim 1 in which a single strip is twisted about its axis.
 5. The method of claim 4 in which the distance between the grip at the twister head and the grip at the entry end is the same as the distance between the grip at the twister head and the grip at the exit end.
 6. The method of claim 5 in which the grips at the entry and exit ends are free to move longitudinally as the strip is twisted while maintaining the predetermined tension.
 7. The method of claim 1 in which a plurality of strips are twisted together.
 8. The method of claim 7 in which the distance between the grip at the twister head and the grip at the entry end is the same as the distance between the grip at the twister head and the grip at the exit end.
 9. The method of claim 8 in which the grips at the entry and exit ends are free to move longitudinally as the strip is twisted while maintaining the predetermined tension.
 10. Apparatus for making an elongated twisted object having the direction of twist reversed at intervals which comprises an entry tensioning stand including strip gripping means, a twister head stand on the exit side of said entry tensioning stand including strip gripping means, an exit tensioning stand on the exit side of said twister head stand including strip gripping means, means for feeding the number of strips desired in the finished object through said stands, said strip being in untwisted form prior to being fed into and gripped by said strip gripping means, resilient means on each of said entry and exit tensioning stands urging their strip gripping means away from said entry tensioning stand to provide a predetermined tensioning force to the strip when clamped by all of said strip gripping means and means for rotating said strip gripping means.
 11. Apparatus according to claim 10 in which each of said tensioning stands includes guides mounted thereon, and a slide supporting said gripping means slidably mounted for longitudiNal movement in said guides, said resilient means including a pair of air cylinders having their axes substantially parallel to the path of travel of said strip and their piston rods connected to said slide.
 12. Apparatus according to claim 11 in which said entry gripping means includes a pair of opposed clamp members, and an air cylinder and piston rod for moving said clamp members with respect to one another; and in which said exit clamping means includes a pair of opposed clamp members each having a beveled strip bearing surface on its inner end, a spring urging each of said clamp members inwardly toward one another, a pair of elongated grip holders on the exit side of said clamp members and one secured for movement with each of said clamp members, springs for biasing said grip holders apart, a resilient grip attached to each grip holder, and an air cylinder and piston rod associated with each grip holder for moving then together.
 13. Apparatus according to claim 12 in which said twister head stand comprises a twister rotor having an axial hole therethrough, and means for rotating said rotor; and said twister head stand gripping means including a pair of opposed radial clamping members one on each side of said axial hole and each having a beveled gripping surface, a roller mounted on the outer end of each radial clamping member with the axis of each roller being transverse to the axis of said rotor hole, a spring urging each clamp member outwardly, a pressure member slidably mounted on said rotor having a cup portion with an internal tapered surface for contacting said rollers and a peripheral groove, a pair of spaced rollers in said peripheral groove, a lever assembly for supporting said spaced rollers, and an air cylinder and piston rod associated with said lever for moving said pressure member to move said clamping members to clamping position.
 14. Apparatus according to claim 13 including a pneumatic control system, said pheumatic control system comprising means for supplying air to said tensioning cylinders to move said slides to their centered position, means then operable for supplying air to said clamping cylinders to cause said clamping means to grip untwisted strip extending between said entry and exit tensioning stands, means then operable to cause air at a predetermined pressure to be present only on the side of the cylinder pistons urging said slides away from the twister head stand, and means operable after twisting of said strip to cause opposite movement of said clamping cylinders to release said strip.
 15. Apparatus according to claim 13 including a pay-off reel at the entry end of said entry tensioning stand for supporting said strip in untwisted form, a take-up reel at the exit end of said exit tensioning stand for supporting said twisted object, and at least four foundations spaced apart between said reels for selectively receiving said stands.
 16. Apparatus according to claim 15 including a pneumatic control system, said pneumatic control system comprising means for supplying air to said tensioning cylinders to move said slides to their centered position, means then operable for supplying air to said clamping cylinders to cause said clamping means to grip untwisted strip extending between said entry and exit tensioning stands, means then operable to cause air at a predetermined pressure to be present only on the side of the cylinder pistons urging said slides away from the twister head stand, and means operable after twisting of said strip to cause opposite movement of said clamping cylinders to release said strip.
 17. Apparatus according to claim 16 in which said pneumatic control system includes four manifold pipe lines extending adjacent said foundations and having a set of sockets adjacent each foundation, a control stand having connections to one set of sockets, and flexible connections between each of said stands and the adjacent set of sockets.
 18. Apparatus according to claim 10 including a pay-off reel at the entry end of said entry tensioning stand for supporting said strip in untwisted form, a take-up reel at the exit end of said exit tensioning stand for supporting said twisted object, and at least four foundations spaced apart between said reels for selectively receiving said stands. 